1. Field of the Invention
The present invention relates to a coordinate input apparatus in an information processing system, and in particular, to a coordinate input apparatus which detects a position in a two-dimensional space so as to input the position as coordinate data, for example, in a host computer of the information processing system.
2. Description of the Prior Art
The coordinate input apparatuses of this kind include an optical coordinate input apparatus in which photoemitters as light sources and photosensors as light receivers paired with the photoemitters are arranged with an input plane (input operation space) therebetween such that the photoemitters oppose to the photosensors in the X and Y directions and a coordinate input apparatus of an induced voltage method in which a great number of sense lines are arranged in the X and Y directions with respect to the input direction so as to form a matrix thereof, thereby sensing induced voltages appearing in said sense lines. These coordinate input apparatuses are generally called touch input apparatuses or touch panels. (Incidentally, in the case of the optical coordinate input apparatus, the input is supplied through an interruption of the light sources and hence the operation to touch the apparatus need not be necessarily effected.)
In the input apparatuses such as the touch panel, regardless of the type thereof described above, an input space of a finger or a position on the panel is detected as data associated with the X and Y coordinates through an input operation so as to input the coordinate data in the host computer or the like.
In the following paragraphs, description will be particularly given of an example of an optical coordinate input apparatus.
In the optical coordinate input apparatus, as described above, the light sources (photoemitters) and light receiving elements (photosensors) paired therewith are arranged so as to oppose to each other, and according to a counter value delivered from a counter circuit, the light sources are sequenctially driven to effect a scanning operation. In this fashion, a sense signal is produced when a light is not received because a light path is interrupted by a coordinate input operation, for example, through a touch of a finger and the light from a photoemitter does not reach the corresponding photosensor. The counter value associated with the sense signal is detected as an input coordinate data.
The coordinate input apparatus of this kind is employed in various manners, for example, the apparatus is mounted on a CRT face of a CRT unit as a terminal of an information processing system so as to effect an input operation by use of a display on the CRT face as a target, or the apparatus is located on a sheet to effect an input operation by tracing an image on the sheet.
Furthermore, particularly, in a case where the coordinate input apparatus is disposed on a CRT face for the use thereof, there appears a parallax between an image displayed as a target on the face and a panel of the coordinate input apparatus generally made of a flat, transparent material, which leads to a problem that coordinate data other than desired coordinate data is inputted.
FIG. 7 is an explanatory diagram useful to explain an occurrence of a parallax which includes a display unit (for example, a CRT) 100, a coordinate input apparatus 200, a display surface 300 of the display unit (for example, a face of the CRT), a display area 400, positions of an eye 500 and 600, a display area P.sub.2 -Q.sub.2 ' on the coordinate input apparatus 200 associated with the eye position 500, and a display area P.sub.2 '-Q.sub.2 on the coordinate input apparatus 200 associated with the eye position 600,
In FIG. 7, when the display surface 300 of the display apparatus 100 becomes apart from the coordinate input apparatus 200, particularly when the display surface 300 is a curved surface like the face of a CRT, depending on the position of the eye of the user, there appears a positional unmatching due to a parallax between a position (coordinate point) of the coordinate input apparatus and the display area 400 of the display apparatus. In this figure, for the eye position 500, a display area P.sub.2 -Q.sub.2 ' results on the coordinate input apparatus 200, whereas for the eye position 600, a display area P.sub.2 '-Q.sub.2 is attained on the coordinate input apparatus 200.
Consequently, for the eye position 500, point P, in the display area 400 of the display apparatus, namely, point P.sub.2 where a line connecting between the eye position 500 and the point P.sub.1 intersects the coordinate input apparatus 200 is not attended with a positional difference; consequently, when a coordinate input operation is effected on the point P.sub.2 of the display apparatus 200, for example, by touching the point P.sub.2 by a finger, th point P.sub.1 as a target in the display apparatus 100 can be inputted as correct coordinate data in a host computer or the like. However, when inputting the point Q.sub.1 of the display apparatus, the input operation is effected by touching point Q.sub.2 ' of the display apparatus, namely, point Q.sub.1 ' apart from the objective point Q.sub.1 by a distance of D corresponds thereto, and as a result, wrong data is inputted.
In order to prevent a wrong data input of the coordinate input apparatus due to the parallax, there has been disclosed, for example, a method by the Japanese Patent Laid-Open No. 62-99824 in which a correction table is employed. According to this method, input point coordinates indicated by an input operation and correction values corresponding to a parallax at the input point are stored in an ROM so as to automatically correct a wrong data input due to the parallax of the input coordinate point.
In addition, the Japanese Patent Laid-Open No. 61-208532 discloses a system which employs an ROM table storing the similar correction values and which includes a hierarchic structure where photoemitters and photosensors of a coordinate input apparatus arranged on a display apparatus are located in the proximity of each other on a curved surface of the face of a CRT as the display apparatus.
However, according to the prior art technology described in the publication above, the detection of the input point coordinates of the coordinate input apparatus is effected in the X-Y matrix disposed in a discrete fashion on a two-dimensional space; consequently, the correction table stores predetermined correction values for each group including a plurality of areas on the two-dimensional plane of the coordinate input apparatus, which leads to a problem that defects of coordinates occur on boundaries where the correction values vary.
Next, referring to the drawings, the mechanism of occurrence of the problem will be described.
FIG. 8 is an explanatory diagram useful to explain an example of a parallax correction table, whereas FIG. 9 is an explanatory diagram useful to explain coordinate data corrected by use of the table.
In FIG. 8, reference numerals 0, 1, 2, etc. correspond to positions of the photosensors and T.sub.11, T.sub.12, . . . , T.sub.21, T.sub.22, . . . , T.sub.31, T.sub.32, etc. indicate respective correction areas.
In this configuration, for example, in the correction area T.sub.11, when a photosensor X-1 of the X coordinate and a photosensor Y-1 of the Y coordinate are inputted through an input operation (the light sources to the photosensors X-1 and Y-1 are interrupted), the coordinates (1, 1) of the input point are corrected as coordinate input data to be (0, 0) since the correction values are X:-1 and Y:-1, and for the coordinates (1, 6), the correction values are X:-1 and Y:+1 and hence the coordinate input values are corrected and are outputted as (0, 7). Incidentally, when the value after the correction is negative (-), 0 is assumed, whereas when the value exceeds the maximum value in the X or Y direction, the corresponding maximym value in the X or Y direction is assumed.
The coordinate input data thus corrected in the correction procedure are shown in FIG. 9. In this figure, the arrows indicate the correction directions.
In FIG. 9, S.sub.11, S.sub.12, . . . , S.sub.21, S.sub.22, . . . , S.sub.31, S.sub.32, etc. denote coordinate input data after the correction. As can be seen from this figure, the erroneous input due to the parallax is corrected by the correction above. However, at positions 2 and 7 in the X direction and at positions 2 and 5 in the Y direction as indicated by the arrows A-D, there occur defects of coordinate input data.
That is, for the coordinate input data, at the X coordinates 2 and 7 and at the Y coordinates 2 and 5, data are missing in any cases.
As shown in FIGS. 8-9, in an apparatus in which the coordinate input data is attained according to a physical arrangement of photoemitters and photosensors (to be referred to as a single-precision coordinate input apparatus herebelow), when an input operation is accomplished astriding two adjacent photosensors, for example, X=2 and X=3, the detection is effected at either X=2 or X=3 according to the priority processing; consequently, for X=2, since the table T.sub.11 of FIG. 8 includes the correction value X:-1, the coordinate input data is assumed to be X=1. On the other hand, for X=3, the correction value in the table T.sub.12 is X:0 and hence the coordinate input value is X=3 without any alteration.
As a result, the coordinate input data for X=2 is not included as data.
As an improvement of the single-precision coordinate input apparatus having the priority processing, the present applicant has already proposed in the Japanese Patent Application No. 62-62158 an apparatus (to be referred to as a double-precision coordinate input apparatus) in which when an input operation is effected astriding two adjacent photosensors, the intermediate point of the two coordinate values is calculated.
However, also in the double-precision coordinate input apparatus, there occur defects of coordinate input data.
According to the prior art technology described above, in an apparatus in which an error of coordinate input data caused by a parallax of the coordinate input apparatus is corrected by use of a correction table including a plurality of areas established in accordance with relative positions between the coordinate input apparatus and the display apparatus, there has been a problem that depending on a difference between the correction values in areas of the correction table, there occur defects of coordinate input data on area boundaries.